Tribo-corona powder application gun

Abstract

The invention provides a gun for spraying a powder onto a work piece to form a coating and includes a pistol-grip housing having an air valve coupled to a source of pressurized air. The housing also supports a source of variable electrical potential. A powder container is disposed in fluid communication with the air valve so that powder within the container may be fluidized by air from the source of pressurized air when the valve is opened. A nozzle is positioned within the housing and includes a central passageway having an open end and disposed in fluid communication with the powder container. The central passageway frictionally imparts a net electrical charge of a first polarity to a first portion of the powder when the first portion of the powder contacts the surface during the spraying. A discrete member is positioned within the central passageway and is capable of imparting a net electrical charge of a second polarity to a second portion of the powder when the second portion of the powder contacts the tubes during the spraying. An emitter rod is positioned within the central passageway and comprises a proximal end and a distal end, where the proximal end is interconnected to the source of variable electrical potential.

What is claimed is:  
     
       1. A gun for spraying a powder onto a work piece to form a coating, said gun comprising: 
       a pistol-grip housing including an air valve coupleable to a source of pressurized air, and supporting a source of variable electrical potential comprising a power supply operatively interconnected between a pressure/electric switch and an adjustable potentiometer wherein said pressure/electric switch is operatively interconnected to and activated by said source of pressurized air and said adjustable potentiometer is interconnected to a voltage indicator having a display positioned on an outer surface of said pistol-grip housing;  
       a powder container disposed in fluid communication with said air valve wherein said powder is fluidized by air from said source of pressurized air when said valve is opened;  
       a nozzle having a central passageway including an open end and disposed in fluid communication with said powder container, said central passageway frictionally imparting a net electrical charge of a first polarity to a first portion of said powder when said first portion of said powder contacts said surface during said spraying;  
       a discrete member disposed within said central passageway and capable of imparting a net electrical charge of a second polarity to a second portion of said powder when said second portion of said powder contacts said tubes during said spraying; and  
       an emitter rod positioned within said central passageway and comprising a proximal end and a distal end wherein said proximal end is interconnected to said source of variable electrical potential.  
     
     
       2. Apparatus according to  claim 1  wherein said power supply comprises an inverter capable of supplying a predetermined DC electrical potential in the range from about 10 kV to about 25 kV. 
     
     
       3. Apparatus according to  claim 1  wherein said pressure/electric switch is operatively interconnected between said power supply and said air valve so that when said air valve is opened a portion of a stream of pressurized air is diverted to engage and actuate said pressure/electric switch. 
     
     
       4. Apparatus according to  claim 1  wherein said emitter rod extends through central passageway and within said discrete tube. 
     
     
       5. Apparatus according to  claim 1  wherein said air valve is interconnected to said source of pressurized air through an air coupler and is actuated by a trigger mounted to said pistol-grip housing. 
     
     
       6. Apparatus according to  claim 5  wherein a tube extends from an exit orifice of said air valve and is operatively coupled to said proximal end of said nozzle and to a pressure/electric switch mounted within said pistol-grip housing and operatively interconnected said power supply so that when said air valve is opened a portion of a stream of pressurized air is diverted to engage and actuate said pressure/electric switch. 
     
     
       7. A gun for spraying a powder onto a work piece to form a coating, said gun comprising: 
       a pistol-grip housing including a trigger actuated air valve coupled to a source of pressurized air and supporting a power supply that is operatively interconnected between said pressure activated switch and an adjustable potentiometer wherein said pressure activated switch is operatively interconnected to and activated by said source of pressurized air and said adjustable potentiometer is interconnected to a voltage indicator having a display positioned on an outer surface of said pistol-grip housing;  
       a powder container disposed in fluid communication with said trigger actuated air valve wherein said powder is fluidized by air from said source of pressurized air when said valve is actuated;  
       a nozzle having a first end through which said fluidized powder is introduced into a central passageway and a second end through which said fluidized powder emerges, said central passageway having at least one charging surface therein made of a first electrically insulated material suitable for electrically charging said powder by friction;  
       a discrete tube disposed within said central passageway, separate from said central passageway, said tube having at least one charging surface thereon made of a second electrically insulated material suitable for electrically charging said powder by friction; and,  
       a corona discharge assembly including an emitter rod positioned in substantially coaxial relation to said central passageway, a power supply positioned within said pistol-grip housing, a pressure activated switch operatively interconnected between said power supply and said trigger actuated air valve, a variable potentiometer positioned in said housing, and said emitter rod.  
     
     
       8. Apparatus according to  claim 7  wherein said power supply comprises an inverter capable of supplying a predetermined DC electrical potential in the range from about 10 kV to about 25 kV. 
     
     
       9. Apparatus according to  claim 7  wherein said pressure/electric switch is operatively interconnected between said power supply and said air valve so that when said air valve is opened a portion of a stream of pressurized air is diverted to engage and actuate said pressure/electric switch. 
     
     
       10. Apparatus according to  claim 7  wherein said emitter rod extends through central passageway and within said discrete tube. 
     
     
       11. Apparatus according to  claim 7  wherein a tube extends from an exit orifice of said air valve and is operatively coupled to said proximal end of said nozzle and to a pressure/electric switch mounted within said pistol-grip housing and operatively interconnected said power supply so that when said air valve is opened a portion of a stream of pressurized air is diverted to engage and actuate said pressure/electric switch.